1. Technical Field
This invention generally relates to bats, such as baseball and softball bats, and more specifically relates to a method of tuning such bats for optimum performance and to bats that are tuned.
2. Background Art
Bats, such as baseball and softball bats, are well known. Many bat manufacturers have attempted to produce more lively bats (bats that would allow players to hit the ball with greater velocity). Such attempts have included the use of composite materials in the structure of tubular bats. Manufacturers thought that the composites would make the bats stiffer and thereby improve their performance. However, stiffer composite bats have generally been less lively than bats produced from more conventional materials, such as aluminum.
Others have attempted to manufacture more lively bats by altering the dimensions of bats made from aluminum, titanium, and composite or combinations thereof. These alterations have generally been done by trial and error, wherein a manufacturer alters the bat dimensions, manufactures a bat, tests the bat""s performance to determine whether it is lively, and begins the process again until a more lively bat is produced. These trial-and-error alterations are expensive and time consuming, and moreover, they are not guaranteed to produce advantageous results. However, such alterations have produced some success. For example, it has been found that titanium and aluminum bats having thin-walled barrels generally perform better than such bats having thick-walled barrels. Even this advance has been limited because bats having thin-walled barrels are generally less durable than bats having thick-walled barrels. Therefore, bat manufacturers have been caught in the difficult position of choosing between greater performance and greater durability.
Another example of an attempt at trial-and-error alterations is U.S. Pat. No. 5,624,115 to Baum, issued Apr. 29, 1997 (the ""115 patent). The ""115 patent discloses a composite bat having a central cavity within the barrel. The ""115 patent also discloses that the nature of the composite layers that form the barrel may be adjusted so that, upon impact the barrel undergoes localized deformation and hoop deformation. The 115xe2x80x2 patent also states that the cavity increases the hoop spring and decreases the local deformation, and that the size and shape of the cavity may be designed to maximize energy transfer to the ball. However, the ""115 patent does not disclose how the energy transfer to a batted ball can be optimized in different bats, and, therefore, its disclosure does not obviate the need for trial-and-error alterations.
The governing authorities in some softball leagues and tournaments have increased the difficulty of the manufacturers"" position. These authorities have banned bats that are too lively because of injuries to infielders produced by high-velocity batted balls. Accordingly, these authorities require that all bats be tested before players use them in official games, thereby assuring that the bats are not too lively. The required tests yield a bat performance factor (BPF), wherein a higher number corresponds to a bat having a greater ability to produce high velocities in batted balls. Typically, these authorities require that the BPF of a bat be no greater than 1.20. Thus, it is now desirable in many instances to make a bat that is lively, but not too lively. Trial-and-error alterations are even more time-consuming and expensive to manufacturers trying to achieve optimum results without producing a bat that is too lively.
Accordingly, there is a need for an improved method of selecting the properties of a bat that will optimize the performance of the bat without significant trial-and-error alterations, and an optimized bat produced by the method that has optimum performance and optimum durability. The present invention fills this need.
The invention includes a method of tuning a bat. The method includes estimating a ball-bat interaction time, Ti, of an impact between a ball and the bat, and tuning at least one desired mode of vibration in the bat produced by the impact. The desired mode of vibration is tuned by selecting a factor and selecting properties of the bat so that a desired mode of vibration has a period approximately equal to Ti multiplied by the factor. In one embodiment the factor is 4/3 so that the period is approximately equal to 4/3 Ti.
Regardless of how a bat is tuned, the bat will store energy, and it will release that energy during subsequent vibrations. However, when a mode of vibration is tuned so that a desired mode of vibration has a period approximately equal to 4/3 Ti, the desired mode of vibration will transfer more of the released energy to the batted ball than if the mode of vibration had some other period. Thus, the desired mode of vibration will release energy more constructively. Furthermore, by tuning the bat in this manner, the cost and time involved in optimizing the performance of a bat is decreased significantly, and a tuned bat, wherein one or more of the select modes is approximately equal to 4/3 Ti has a desirable BPF. The method of the present invention also allows the wall thickness of a tubular bat to be maximized for a particular BPF, thereby maximizing durability of the bat.
Properties that may be selected in tuning the bat include modulus of elasticity, material density, and wall thickness for tubular bats. The modulus of elasticity may be selected by selecting the material of the bat, such as aluminum or titanium. In a composite bat, this may be done by selecting the fiber type or the angle of the fibers with respect to a longitudinal axis of the bat. For example, fibers may be selected that have from about 33 million psi modulus to about 120 million psi modulus. The density may be selected by selecting the material type or, in a composite bat, by selecting the volumetric fiber density. Moreover, the weight of the tip cap and the butt cap can be selected, and will affect the period of axial bending modes of vibration.
Typically, the selection of wall thickness, the fiber type, and the fiber angle will have the greatest impact on the periods of vibration because they can vary greatly, and they affect the overall stiffness of the bat. Of these, wall thickness typically can have the greatest effect. Although the density will affect the periods of vibration, it cannot be varied greatly after a general type of material has been chosen. For example, once composite materials are selected, the density cannot be varied greatly because the density between different composites does not vary greatly.
Typically, the first hoop mode of vibration will impart the most energy to a batted ball, so its optimization is given first priority during tuning of the bat. However, other modes of vibration, such as an axial bending mode of vibration may also be tuned to have a period approximately equal to 4/3 Ti. This is particularly true in composite bats where selecting the fiber angles can yield a different modulus of elasticity in the hoop direction than in the direction of the longitudinal axis of the bat. Thus, a tuned bat may have a tuned mode from each of multiple types of vibrations, such as axial and hoop vibration.
The foregoing and other features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.